How to Edit M4B Metadata, Cover Art, and Chapters on a Mac

The audiobook itself is finished and it plays. What is wrong is everything printed around it: the library shelf credits the author as “Audible”, the cover belongs to a different book entirely, and Chapter 4 is called P?edmluva.

Nothing is broken. Everything is wrong. AudioBo fixes all of it in one window — title, author, cover, every chapter name — and writes it back without touching the audio. The page below is that, plus the by-hand routes and their traps.

And Apple Books, the app you are looking at it in, is going to be almost no help — which is worth explaining before you spend an evening looking for a menu item that does not exist. The rest of this page is the machinery: what Books really does with your file, what changing the file involves, and why the cover and the chapter titles went wrong in the first place.

What Apple Books actually lets you change

Two things, and both of them happen to a copy.

You can rename the book, and you can replace its cover. That is the entire list. Neither change reaches the file you dragged in, because Books took a copy of it at import and works on that one instead — your book, wherever you keep it, still has the same wrong author printed inside it.

On macOS 26.6, the only editing affordances in the Books app’s own string table are Rename — which changes the displayed title — and Change Cover, which carries the warning “The original cover will be permanently removed.”

There is no editable author field. No narrator, no series, no year, no genre, no chapter titles. Searching Books’ localized strings for “Get Info” or “Edit Metadata” returns nothing at all, because those screens are not in the app.

Then there is the part that catches people who did find Rename and Change Cover and thought they had won.

Books does not edit your file. When you drop an audiobook in, Books copies it into its own container and works on the copy.

Want to see the copies? They are sitting on your own disk:

~/Library/Containers/com.apple.BKAgentService/Data/Documents/iBooks/Books/Audiobooks/

Inside are folders named sha1-<hash>, each holding the .m4b files Books imported. Rename and Change Cover act on those. Your original, wherever you keep it, is untouched — so the moment you copy the book to a phone, hand it to Plex, or move to a new Mac, the tags are exactly as wrong as they were.

If you want the fix to travel with the file, you have to change the file.

Changing the file itself takes seconds, and nothing is re-encoded

Editing an audiobook is not the same as rebuilding one. The sound is one thing inside the file; the printed matter — title, author, cover, chapter list — is another, sitting next to it. Change the second and the first is not touched: not recorded again, not compressed again, not a little worse every time you fix a typo. It is nearer to putting a new label on a jar than to cooking the contents twice.

This is the part that stops people from trying, so here are the numbers.

An M4B is AAC audio in an MPEG-4 container. The audio sits in one atom; the tags, the cover, and the chapter table sit in others. Rewriting metadata means rewriting the small atoms and copying the big one across untouched. Nothing is decoded, nothing is re-encoded, and there is no generation loss to worry about — the question does not arise.

Want to run it yourself? Here is the command, and what it cost. I built a two-hour M4B, 59 MB, and rewrote the title, the author, and every chapter title with a stream copy:

ffmpeg -i book.m4b -i chapters.txt -map 0:a -map 0:v? -map_metadata 1 \
  -map_chapters 1 -c copy -disposition:v:0 attached_pic \
  -brand "M4B " -metadata media_type=2 -f mp4 fixed.m4b

That finished in 0.63 seconds, and the audio stream MD5 was byte-for-byte identical to the source. On a real ten-hour audiobook the operation is bounded by how fast your disk copies the file, not by anything to do with audio.

The chapter file is plain text in ffmpeg’s metadata format:

;FFMETADATA1
title=Osudy dobrého vojáka Švejka
artist=Jaroslav Hašek
[CHAPTER]
TIMEBASE=1/1000
START=0
END=20000
title=Předmluva

Non-ASCII titles survive this intact — I checked with Czech and Ukrainian chapter names in the same pass. So does an embedded cover, added in the same command:

ffmpeg -i book.m4b -i cover.jpg -map 0:a -map 1:v -disposition:v:0 attached_pic \
  -c copy -f mp4 fixed.m4b

Two honest caveats before you commit to this route.

Name the cover stream or lose it. -map 0:a on its own selects the audio and nothing else, and the artwork leaves with everything else you did not name. -map 0:v? picks the picture back up, and the ? makes it optional so the command still runs on a book that never had a cover. I ran it both ways on the same file to be sure.

The audiobook brand is yours to ask for. Left to itself, -f mp4 writes a container brand of isom — I checked, even with .m4b on the filename — and -f ipod gives you M4A , which is not better. That is what the -brand "M4B " in the command above is for, with -metadata media_type=2 beside it setting the audiobook flag; leave the pair off and the repair hands you back a music file wearing an audiobook’s name. Whether the brand matters depends on which app you are feeding — that argument belongs to what an M4B file actually is. Chapters, at least, come out fine: ffmpeg writes both of the formats players look for, which is the other half of the chapter problem.

For one book, this is the correct tool and you should use it. For the fortieth chapter title in a book whose narrator typed everything in caps, it is a text file you are editing blind.

The refresh trap: Books keeps showing the old title

You edit the file. You go back to Books. The old title is still there.

This is the single most common “it didn’t work” report, and it is not a failure of the edit. Books is still playing the copy it made at import time, which is a different file that you did not change.

The fix is a delete and a re-import, in that order — and there is a hazard in it. When you delete a sideloaded audiobook, Books tells you plainly: “Audiobooks not purchased from the Audiobook Store will be permanently deleted.” That is the only copy Books has. If your original is not sitting safely somewhere outside the Books library, deleting it inside Books is a deletion, not a removal.

So: keep your masters in a folder you control, import copies into Books, and treat the Books library as a display case rather than storage.

Why the cover was wrong to begin with

Cover art has more failure modes than the rest of the metadata combined, and they look identical from the outside.

In ordinary words, one of three things has happened. Either there is no picture inside your book at all, and the app has been showing you one that simply lies beside it in the same folder; or there was a picture inside and a tool that only cared about the audio dropped it on the way through; or Apple Books changed it for itself and for nobody else. The first two are about your file. The third never was.

There is no cover in the file, and the app is showing a folder image. Many players fall back to a cover.jpg or folder.jpg sitting next to the audio. Move the file and the art vanishes; put a different book in that folder and it inherits a stranger’s artwork. AudioBo changed its precedence in 1.2.9 so the cover embedded inside the file always wins over a neighboring image, with the folder image used only when the file itself has none — which also fixed a stale cover from the previous book turning up after New Book.

The art was stripped by a tool that was only thinking about audio. See the -map 0:a case above. This is also the reason chapter-split files sometimes come out blank, which the splitting guide covers where it belongs.

Books changed it, and only for Books. Change Cover acts on the copy in Books’ container, and it warns you that the original cover will be permanently removed. Nothing about your file changed, which is why the old cover comes back the next time you import it somewhere.

An embedded cover is not a file reference: the JPEG or PNG rides inside the container itself, which is why the art travels when the file does.

Check your own book: one command tells you whether there is a picture inside it at all.

ffprobe -v error -show_entries stream=index,codec_type,codec_name yourbook.m4b

An mjpeg or png video stream in that list means the art is genuinely in the file. Nothing but audio means whatever you have been looking at came from somewhere else.

Chapter titles that came back as symbols

P�edmluva. Ðîçä³ë ïåðøèé. Boxes, question marks, accented letters that were never in the original.

The text is not lost. Every letter of the original title is still in the file — it was written down using one alphabet table and is being read back with a different one, so each piece of nonsense on the screen is a correct letter decoded the wrong way.

The cause is mundane and worth knowing, because it tells you what can and cannot be recovered. The chapter titles were written in a legacy single-byte encoding — CP1250 for Czech, Polish, and Hungarian, CP1251 for Russian and Ukrainian — rather than UTF-8, and every modern reader interprets those bytes as UTF-8 and gets nonsense. I stored the Czech word Předmluva as CP1250 bytes in a test file and read it back with a UTF-8 reader: P, a replacement character, edmluva. The Ukrainian Розділ перший written as CP1251 and read as Western European comes back as Ðîçä³ë ïåðøèé. Exactly the symptom.

Decoding those bytes with the right table restores the title perfectly. What makes this miserable by hand is volume: thirty-five chapters means thirty-five retypings in a language you may not speak, in a text editor, without preview.

AudioBo detects and repairs this class of damage automatically on import as of version 1.3.4 — its release notes name Czech and other Central-European titles specifically, along with some Russian and Ukrainian files. You open the book and the titles are already right, which is the only sane place for a fix like this to live.

That is also the point where a dedicated editor stops being a convenience.

What AudioBo does about tags, covers, and chapter names

What you get is one window over the book you already have. The title, the author, the cover and the whole list of chapter names are in front of you; you correct what is wrong, and one keystroke writes it back into the file you opened — the original, not a copy, and with the audio left alone. Paste in a new cover from anywhere, or drag the one that is already there out to Finder if you want to keep it first. Rename forty chapter titles in a single pass, and read the before-and-after of your own change before you commit to it. Titles that arrived as symbols are already repaired by the time you look at them.

Books you keep as MP3 or FLAC rather than M4B go through the same window, so a mixed shelf is not a separate problem. And if the metadata is missing rather than wrong, the app can go and fetch it instead of you typing it in.

AudioBo is a Mac app from the Mac App Store, and there is a demo build if you want to try it on your worst file first.

If you do want the mechanical version: since 1.2.2, ⌘U writes edited tags, cover art, and chapter names straight back into the original file with no re-encoding, and it works on M4B, M4A, MP3, FLAC, OGG, and AIFF alike. 1.2.7 made that pass noticeably faster on large books and fixed fields that used to survive being cleared — Description, Summary, Series, the sort fields, Comment, Copyright, Encoded By — and 1.2.5 gave the Update Metadata button a clear reason to show when a file cannot be modified, plus an automatic permissions fix for files that arrived via iCloud sharing.

For the cover specifically: paste any image straight onto it with ⌘V since 1.3.0, drag the existing one out to Finder to save it since 1.2.4, or copy and export it since 1.3.1. For forty chapter titles at once, the Regex tab in Batch Rename arrived in 1.3.2 with a live before-and-after preview, which is the difference between a find-and-replace you can trust and one you run twice. Sort order is handled in the same place: AudioBo already files The Hobbit under H and authors by last name, and 1.3.4 added manual Sort Title As and Sort Author As fields under Title and Author in Edit Book. And if the metadata is missing rather than mangled, fetching it from Audible or Apple Books is usually faster than typing it.

The limit is worth stating in the same breath: AudioBo builds and repairs the file, and it cannot make a player display something that player does not support — Apple Books ignores per-chapter covers however correctly they are stored, which is the next section. It does not remove DRM either, so a protected download from Audible or the iTunes Store is out of its reach whatever its tags say.

Per-chapter cover images in AudioBo, and the honest caveat

Some books want more than one picture. This is the small feature that allows it — and whether you ever see the result depends entirely on where you listen, so read to the end of the section before you start.

Since 1.3.4, any single chapter can carry its own cover image — useful for a prologue, an interview, or each book in an omnibus. Right-click a chapter and choose Set Chapter Cover, or drag an image onto it; they are all managed under Edit Book → Change Covers, and chapters you leave alone keep the book’s main cover.

Now the part worth saying before you spend an hour choosing artwork: Apple Books on Mac will not show you any of it. AudioBo’s own release notes say so — the covers are saved into the file either way, and players that support them display them, but Books draws the book cover and nothing else. If Books is where you listen, this feature is invisible to you.

What this page does not fix

If the file came from Audible or the iTunes Store and is still protected, none of this applies — the tags are not the obstacle. AudioBo does not remove DRM, and the M4B to MP3 guide carries that discussion properly.

If your file has no chapters at all rather than badly named ones, this is the wrong repair: diagnosing a chapterless M4B is a different question with a different answer. And if what you want is one file per chapter instead of one file with better chapter names, splitting an M4B goes the other way.